During a 10 year period, 14 out of 227 patients (6.2%) undergoing continuous ambulatory peritoneal dialysis (CAPD) developed permanent loss of ultrafiltration capacity (UFC). The risk of UFC loss increased from 2.6% after one year to 30.9% after six years of treatment. A six hour, single dwell study with glucose 3.86% dialysis fluid was carried out in nine of the UFC loss patients and in 18 CAPD patients with normal UFC. Intraperitoneal dialysate volumes were calculated using 131I-tagged albumin (RISA) as volume marker with a correction applied for its elimination from the peritoneal cavity. The RISA elimination coefficient (KE), which can serve as an estimation of the upper limit of the lymphatic flow, was also calculated. Diffusive mass transport coefficients (KBD) for investigated solutes (glucose, creatinine, urea, potassium, total protein, albumin and beta 2-microglobulin) were calculated during a period of dialysate isovolemia. Two patterns of UFC loss were observed: (a) seven patients had high KBD values for small solutes resulting in rapid uptake of glucose, whereas KBD values for proteins were normal; (b) two patients had normal KBD values but a threefold increase both in the fluid reabsorption rate and KE. We conclude that loss of the osmotic driving force (due to increased diffusive mass transport for small solutes) and increased fluid reabsorption (possibly due to increased lymphatic reabsorption) are the two major causes of permanent loss of UFC in CAPD patients.

To investigate the relationship between dialysate glucose concentration and peritoneal fluid and solute transport parameters, 41 six-hour single dwell studies with standard glucose-based dialysis fluids containing 1.36% (N = 9), 2.27% (N = 9) and 3.86% (N = 23) anhydrous glucose were carried out in 33 clinically-stable continuous ambulatory peritoneal dialysis (CAPD) patients. Intraperitoneal dialysate volumes (VD) were determined from the dilution of 131I-albumin with a correction applied for its elimination from the peritoneal cavity (KE, ml/min). Diffusive mass transport coefficients (KBD) were calculated from aqueous solute concentrations (with a correction applied for the plasma protein concentration and, for electrolytes, also for the Donnan factor) during a period of dialysate isovolemia. The intraperitoneal amount calculated to be transported by diffusion was subtracted from the measured total amount of solutes in the dialysate, yielding an estimate of non-diffusive solute transport. The intraperitoneal dialysate volume over time curve was characterized by: initial net ultrafiltration (lasting on average 92 min, 160 min and 197 min and with maximum mean net ultrafiltration rates 6 ml/min, 8 ml/min and 14 ml/min, respectively, for the 1.36%, 2.27% and 3.86% solutions); dialysate isovolemia (lasting about 120 min for all three solutions) and fluid reabsorption (rate about 1 ml/min for all three solutions). KBD for glucose, potassium, creatinine, urea and total protein did not differ between the three solutions and the fractional absorption of glucose was almost identical for the three glucose solutions, indicating that the diffusive transport properties of the peritoneum is not influenced by the initial concentration of glucose or the ultrafiltration flow rate. About 50% of the total absorption of glucose occurred during the first 90 minutes of the dwell. The mean percentage of the initial amount of glucose which had been absorbed (%GA) at time t during the dwell could be described (r = 0.999) for all three solutions using the experimental formula %GA = 85 - 75.7 * e-0.005*t. After 360 minutes, about 75% of the initial intraperitoneal glucose amount had been absorbed corresponding to a mean (+/- SD) energy supply of 75 +/- 6 kcal, 131 +/- 18 kcal and 211 +/- 26 kcal for the three solutions. Non-diffusive (that is, mainly convective) transport was almost negligible for the less hypertonic solutions while it was estimated to account for 30 to 40% of the total peritoneal transport of urea, creatinine and potassium during the first 60 minutes of the 3.86% exchange.

The Valsalva manoeuvre (VM), a forced expiratory effort against a closed airway, has a wide range of applications in several medical disciplines, including diagnosing heart problems or autonomic nervous system deficiencies. The changes of the intrathoracic and intra-abdominal pressure associated with the manoeuvre result in a complex cardiovascular response with a concomitant action of several regulatory mechanisms. As the main aim of the reflex mechanisms is to control the arterial blood pressure (BP), their action is based primarily on signals from baroreceptors, although they also reflect the activity of pulmonary stretch receptors and, to a lower degree, chemoreceptors, with different mechanisms acting either in synergism or in antagonism depending on the phase of the manoeuvre. A variety of abnormal responses to the VM can be seen in patients with different conditions. Based on the arterial BP and heart rate changes during and after the manoeuvre several dysfunctions can be hence diagnosed or confirmed. The nature of the cardiovascular response to the manoeuvre depends, however, not only on the shape of the cardiovascular system and the autonomic function of the given patient, but also on a number of technical factors related to the execution of the manoeuvre including the duration and level of strain, the body position or breathing pattern. This review of the literature provides a comprehensive analysis of the physiology and pathophysiology of the VM and an overview of its applications. A number of clinical examples of normal and abnormal haemodynamic response to the manoeuvre have been also provided.

The process of water reabsorption from the peritoneal cavity into the surrounding tissue substantially decreases the net ultrafiltration in patients on peritoneal dialysis. The goal of this study was to propose a mathematical model based on data from clinical studies and animal experiments to describe the changes in absorption rate, interstitial hydrostatic pressure, and tissue hydration caused by increased intraperitoneal pressure after the initiation of peritoneal dialysis. The model describes water transport through a deformable, porous tissue after infusion of isotonic solution into the peritoneal cavity. Blood capillary and lymphatic vessels are assumed to be uniformly distributed within the tissue. Starling's law is applied for a description of fluid transport through the capillary wall, and the transport within the interstitium is modeled by Darcy's law. Transport parameters such as interstitial fluid volume ratio, tissue hydraulic conductance, and lymphatic absorption in the tissue are dependent on local interstitial pressure. Numerical simulations show the strong dependence of fluid absorption and tissue hydration on the values of intraperitoneal pressure. Our results predict that in the steady state only approximately 20-40% of the fluid that flows into the tissue from the peritoneal cavity is absorbed by the lymphatics situated in the tissue, whereas the larger (60-80%) part of the fluid is absorbed by the blood capillaries.

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To investigate possible effects of glucose concentration, dwell time, and peritoneal reabsorption on the combined diffusive and convective peritoneal solute transport, dialysate to plasma concentration ratios (D/P) and solute clearances were evaluated for 6-h peritoneal dwell studies with 1.36, 2.27, and 3.86% glucose solutions. The diffusive mass transport coefficient, KBD, and sieving coefficient, S, were estimated using the Babb-Randerson-Farrell model of peritoneal transport. Dialysate volumes over time and peritoneal reabsorption rates, KE, were assessed using radiolabeled iodinated serum albumin (RISA). The transport parameters were estimated with and without peritoneal reabsorption of solutes taken into account. To test the stability of the transport parameters throughout a single peritoneal dwell, KBD and S values were estimated for the initial 3-120 min, the final 120-360 min, and the entire 3-360 min dwell period for dialysis with 3.86% glucose solution. The transport parameters did not differ between the three dialysis fluids although clearances of small solutes were higher with the 3.86% solution. Values of KBD, but not S, were dependent on the correction for peritoneal reabsorption of solutes. Computer simulations showed that S could be estimated even with the 1.36% glucose solution. A significant change of the transport parameters, with increased values of KBD during the initial period of the dwell, was found for urea, potassium, sodium, and total protein during dialysis with the 3.86% solution. S values for urea and potassium were close to 1 during the initial period whereas unphysical (higher than 1) S values were found for the whole dwell period. The transient increase of KBD during the initial part of the dwell may reflect changes in the peritoneal barrier possibly induced by fresh dialysis fluid. In conclusion, the transport parameters KBD and S are not influenced by the concentration of glucose in the dialysis fluid. Moreover, the estimation of KBD but not of S is dependent on the assumed rate of peritoneal reabsorption. Finally, the current results challenge the assumption that KBD and S are constant throughout a peritoneal dialysis exchange.

To quantitatively evaluate peritoneal sodium transport, the diffusive mass transport coefficient (KBD) and sieving coefficient (S), as well as the mass of sodium transported by diffusion (DM), by convection (CM) and by fluid absorption (AM) and the total sodium mass removed (RM) were calculated during a series of single dwell studies in CAPD patients. A six-hour dwell study was performed in 68 patients using 2 liter of 1.36% (N = 13), 2.27% (N = 9) or 3.86% (N = 46) glucose dialysis fluid with 131I-albumin as the intraperitoneal volume marker. The patients in whom the 3.86% glucose dialysis fluid was applied were further divided into four transport groups according to a modified peritoneal equilibration test: high (H), high-average (H-A), low-average (L-A), and low (L) transport. There was no significant difference in KBD nor in S for sodium among different solutions. However, the removed sodium mass (RM) was significantly higher in the 3.86% (70.5 +/- 31.5 mmol) and 2.27% (36.0 +/- 21.0 mmol) solutions as compared to that of the 1.36% (-1.8 +/- 26 mmol) solution mainly due to increased both CM and DM. In general, CM was twice as high as DM. AM substantially decreased sodium removal. Among the different transport groups, the KBD and S values for sodium were significantly higher in the H group as compared to the other transport groups (both P < 0.05). However, RM was significantly lower in the H group mainly due to higher AM. Using a 3.86% glucose solution, the D/P for sodium was found to be significantly different (but only after 120 min of the dwell) between all the different transport groups. In conclusion, sodium removal in CAPD is strongly related to the fluid removal. The ultrafiltration induced convective transport (CM) and peritoneal absorption of sodium (AM) were of similar magnitude and were twice as high as the diffusive transport (DM) and both play an important role in the peritoneal sodium balance. A D/P for sodium using the 3.86% glucose solution, especially at the end of the dwell, can be used to discriminate between different transport categories of patients. High transport patients have a poor fluid and sodium removal that are likely to affect their clinical outcome.

It has recently been recommended that the peritoneal dialysate volume should in general be increased to increase the peritoneal small solute clearances. However, the net ultrafiltration volume may decrease due to higher intraperitoneal hydrostatic pressure (IPP) and higher peritoneal fluid absorption induced by higher fill volume. In the present study, we investigated the effects of increasing the fill volume on peritoneal fluid and solute transport. A four-hour dwell study with frequent dialysate and blood sampling was performed in 32 male Sprague-Dawley rats using 16 ml, 25 ml, 30 ml or 40 ml (8 rats in each group) of 3.86% glucose solution with 131I albumin as an intraperitoneal volume marker. The peritoneal transport of fluid, glucose, urea, sodium, potassium, phosphate and total protein as well as IPP with different fill volume were evaluated. The IPP and peritoneal fluid absorption rate (as estimated from the 131I albumin elimination coefficient, KE) significantly increased with increase in fill volume (P < 0.05), whereas the direct lymphatic absorption did not change with increasing fill volume. There was a strong correlation between IPP and KE. However, the net ultrafiltration volume was significantly higher in the high fill volume groups compared to the low fill volume groups, mainly due to a better maintenance of the dialysate to plasma glucose concentration gradient in the high fill volume groups. There was no significant difference in the diffusive mass transport coefficients (KBD) and sieving coefficients for any of the investigated solutes, although KBD values tended to be lower in the 16 ml group. The clearances for small solutes increased with increased fill volume, although these increases were slightly smaller than predicted from the increase in fill volume. We conclude that: (1) An increase in dialysate fill volume using 3.86% glucose solution results in higher intraperitoneal hydrostatic pressure and higher peritoneal fluid absorption, but, on the other hand, a higher net ultrafiltration; (2) The increase in net ultrafiltration with increased fill volume is mainly due to a better maintenance of glucose concentration in the dialysate, inducing an increased transcapillary ultrafiltration rate; (3) Solute clearances increase although not quite to the same extent as predicted from the increase in fill volume. Our results indicate that decreased net ultrafiltration volume associated with higher dialysate fill volume (due to higher IPP and higher peritoneal fluid absorption) could be avoided if hypertonic glucose solutions are used.